Precession of magnetization induced by pulsed optical excitation is observed in a ferromagnetic semiconductor (Ga,Mn)As by time-resolved magneto-optical measurements. It appears as complicated oscillations of a polarization plane of linearly polarized probe pulses, but is reproduced by gyromagnetic theory incorporating an impulsive change in an effective magnetic field due to a change in the magnetic anisotropy. The shape of the impulse suggests a significant nonthermal contribution of photogenerated carriers to the change in anisotropy through spin-orbit interaction.

The magnetic and ferroelectric properties of multiferroic RMn 2 O 5 (R = Y, Tb, Ho, Er, Tm) are reviewed based on recent neutron diffraction and dielectric measurements. Successive phase transitions of magnetic and dielectric ordering were found to occur simultaneously in this system. The characteristic magnetic ordering of the system exhibits an incommensurate-commensurate phase transition, and again transitions to an incommensurate phase. Special attention is given to the magnetic structure in order to discuss the mechanism for the introduction of ferroelectric polarization. For all the compounds examined, the spin configuration for Mn 4+ and Mn 3+ ions in the commensurate magnetic phase, where spontaneous electric polarization occurs, was determined to be a transverse spiral spin structure propagating along the c-axis. By contrast, the alignment of the induced 4f moment of R 3+ ions showed variation, depending on the character of each of the elements. Corresponding responses to external fields such as a magnetic field, hydrostatic pressure etc at low temperature are strongly dependent on the rare earth element present in the RMn 2 O 5 system. The so-called colossal magnetoelectric effect in this system can be easily interpreted by the phase transition from the magnetic incommensurate and weak ferroelectric phase to the commensurate and ferroelectric phase.

Nanoporous metal materials with many potential applications have been synthesized by a chemical dealloying approach. The fabrication of nanoporous metal nanoparticles (NPs), however, is still challenging due to the difficulties in producing suitable nanoscale precursors. Herein, nanoporous Co NPs of 31 nm have been successfully prepared by dealloying Co-Al NPs, and surprisingly they possess micropores in a range from 0.7 to 1.7 nm and a large surface area of 50 m(2) g(-1). The crystalline size of the microporous NPs is 2-5 nm. Through the passivation process, the microporous Co NPs covered with CoO (Co@CoO) are generated as a result of the surface oxidation of Co. They exhibit better microwave absorption properties than their nonporous counterpart. An enhanced reflection loss (RL) value of -90.2 dB is obtained for the microporous Co@CoO NPs with a thickness of merely 1.3 mm. The absorption bandwidth corresponding to the RL below -10 dB reaches 7.2 GHz. The microwave absorption mechanism is discussed in terms of micropore morphology, core@shell structure and nanostructure. This novel microporous material may open new routes for designing high performance microwave absorbers.

Co/C nanoparticles with low graphitization degree that have been prepared by an arc plasma method using methane as the carbon source exhibit high microwave absorption properties.

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